People need folic acid to make DNA and normal red blood cells, and the growing fetus must have it for the proper development of the nervous system. Bacteria must also have folic acid so they can carry out important functions within the cell. Bacteria can make folic acid, however, while people cannot.
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Both humans and bacteria need folic acid to grow. While folic acid can cross the membrane of a human cell and enter the cell, it cannot cross the cell wall of bacteria, according to Charles Ophardt, Ph.D., Emeritus Professor of the Department of Chemistry at Elmhurst College in the “Virtual Chembook.” Thus, bacteria have to make their own folic acid. They will then use the folic acid to make DNA, RNA and methionine. Methionine is an amino acid that is used to make various substances like cysteine, another amino acid, and S-adenosyl methionine, a substance used in many biochemical reactions.
How Bacteria Make Folic Acid
Bacteria make their own folic acid by taking PABA, short for p-aminobenzoic acid, and adding a substance called pteridine to form dihydropteroic acid. Then they add glutamic acid to make dihydrofolic acid and use an enzyme called dihydrofolate reductase to make tetrahydrofolic acid, as explained by B. E. Nardell, Ph.D. of the Department of Pharmacology at Ross University School of Medicine in “Antimicrobial Chemotherapy.” Enzymes are a type of protein that the cells must use to make a reaction go fast enough. Tetrahydrofolic acid is the form of folic acid that the bacterial cells need.
Antibacterial Medication and Folic Acid
Humans cannot make folic acid because we do not have the enzymes that are needed to make it, and so we have to get it in the diet or in dietary supplements. This also means, however, that one type of medication that can be used to fight bacteria are medications that interfere with the creation of folic acid. This type of medication includes the sulfonamides and trimethoprim, explains Matthew Levison, M.D., Professor of Public Health at Drexel University in “The Merck Manual for Healthcare Professionals.” The sulfonamides interfere with the enzyme dihydropteroate synthetase, needed to make dihydropteroic acid, while trimethoprim interferes with dihydrofolate reductase.
Bacteriostatic and Bactericidal
The sulfonamides are bacteriostatic; that is, they interfere with the growth of bacteria, but they do not kill them, writes Warren Levinson, M.D., Ph.D., Professor of Microbiology at the University of California in “Review of Medical Microbiology and Immunology.” Thus, the bacteria can grow when the person with the bacterial infection stops taking the sulfonamide medication, unless their white blood cells can kill them. Taking a sulfonamide along with trimethoprim kills bacteria; this combination is called bactericidal. The two medications kill because they work at two different places in the chemical pathway that creates folic acid.